The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for formatting a disc within a disc drive. More specifically, the present invention is directed toward the track density as it relates to track misregistration within a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The methods for positioning the transducers can generally be grouped into two categories. Disc drives with linear actuators move the transducer linearly generally along a radial line to position the transducers over the various tracks on the information storage disc. Disc drives also have rotary actuators which are mounted to the base of the disc drive for arcuate movement of the transducers across the tracks of the information storage disc. Rotary actuators position transducers by rotationally moving them to a specified location on an information recording disc. A rotary actuator positions the transducer quickly and precisely. For example, the rotary actuator moves the transducer at 20xc2x0 during a long seek. The rotary actuator undergoes a maximum of 90 G""s of force when moved.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
One constant goal associated with disc drives is to increase the amount of data that can be stored on the disc drive. There are, of course, many techniques for increasing the amount of data on a disc drive. One of the techniques is to increase the number of tracks per inch that are positioned on the surface of a disc. In other words, the number of tracks per inch (xe2x80x9cTPIxe2x80x9d) is increased. Another way of saying the same thing is that the track density is increased.
Increasing the track density must be balance against other problems within the disc drive. One of the problems is increased error rates due to track misregistration. Track misregistration is interference due to the inability of a recording system to maintain the relative positions of the heads and the data track on the media exactly. In a disc drive, the imperfect reproducibility of the moving-head positioning system and differential thermal expansion are among the causes of misregistration. Other causes of track misregistration are windage and the amount of vibration of the disc itself. Windage and vibration generally have a more pronounced effect at the outer tracks on the disc. The greater relative motion between the disc and transducing head near the outer edge of the disc provides for increased windage at the outer diameter of the disc. In fact, as the actuator and attached transducers are moved from the inner diameter to the outer diameter, the windage effect becomes progressively more pronounced.
Vibration also has a more pronounced effect at the outer diameter. The disc is attached to a hub at its inner diameter. The edge of the disc, therefore, is attached more like a cantilevered beam at the inner diameter. As with a cantilevered beam, vibration effects are more pronounced the further from the attachment point. In other words, if the disc is vibrating, the vibration will generally be more pronounced at the outer diameter. Thus, if all other factors remained equal, track misregistration will be higher at the outer diameter than at the inner diameter.
In the past, disc drives were designed with the knowledge that the percentage of occurrences of track misregistration was generally the worst at the outer diameter of the disc. As a result, the track density at the outer diameter of the disc was one of the principal influences in hard disc drive design. Designers knew that by controlling track misregistration the number of resulting read or write errors could also be controlled. In practice, errors occur if the track misregistration is approximately greater than 12% of the track width. Designers typically de signed the disc drive so that the discs had a constant track density across the surface or the recording surface of the disc. In order to ensure that no more than 12% track misregistration occurred, designers would select a track density at the outer diameter that would produce no more than 12% or some other selected percentage of track misregistration. This track density would then be used to write across the surface of the disc. In essence, designers of the disc drives wrote the tracks on the disc at a constant track density so that when the worst case appeared at the outer diameter of the tracks, the read and write channel could accommodate the worst case without producing excessive read or write errors. The problem with this scheme is that it limits the amount of data that can be stored on the disc. In addition, it fails to consider that more data could be written on the inner diameter to increase the capacity of the disc and the disc drive. Furthermore, more errors occur on the outer diameter than on the inner diameter and, therefore, you do not have a uniform distribution of read or write errors across the surface of the disc.
Techniques have been developed to minimize the track misregistration problems. The method and apparatus to correct for read and write element misregistration offsets was developed by Brown in U.S. Pat. No. 5,682,274. Improving the air flow in hard disc drive (HDD) to reduce the track misregistration (TMR) budget was used by the Freeman U.S. Pat. No. 4,147,229. The method to reduce disc flutter non-repeatable runout (NRRO) was introduced by Imai. Zero acceleration path (ZAP) method to reduce repeatable runout (RRO) by Szita.
All of the above methods can significantly improve the TMR in HDD applications. Especially the ZAP method, it makes the RRO become not the major contributor for TMR. However, this makes the NRRO component in TMR become more outstanding. All of the above methods and present servo track writing process did not consider the difference of TMR along the media radius. Contributions from windage effects, disc flutter, microjog compensation error, mechanical resonances make the TMR at outer diameter (OD) much worse than inner diameter (ID). The example will be described in the next section.
What is needed is a disc drive having additional capacity. What is needed is disc for a disc drive which allows additional information to be stored on the disc drive. Furthermore, the disc should be formatted to allow for additional data to be stored on the disc. What is also needed is a disc drive that limits the amount of read and write errors that occur so that the access times to information including customer data remains low. What is also needed is a disc and disc drive that does not allow the occurrence of track misregistration to climb over a selected percentage. A method and apparatus are also needed which can be accommodated using manufacturing techniques close to current manufacturing techniques.
A disc drive includes a base, and a disc rotatably attached to the base. The disc has an inner diameter and an outer diameter and a plurality of tracks. Information is written on the plurality of tracks. The plurality of tracks are written at a variable track pitch. The tracks positioned near the outer diameter are wider in pitch than the tracks positioned near the inner diameter. The plurality of tracks further include a first group of tracks written at a first track pitch, and a second group of tracks written at a second track pitch. The first group of tracks has a greater track pitch than the second group of tracks. The first group of tracks is positioned at a greater radial distance from the center of the disc than the first group of tracks. The first group of tracks or the second group of tracks has a greater track pitch than the other of the first group of tracks or the second group of tracks. Furthermore, the track pitch of each of the first group and the second group of tracks is selected such that the percentage of track misregistration for each group will be substantially the same. The track pitch is varied to keep the percentage of track misregistration for each group substantially the same. The disc drive also includes an actuator having a transducer for reading and writing to at least two of the plurality of tracks on the disc. The transducer writes data at different frequencies.
Also disclosed is a disc for a disc drive including a first surface, a second surface, and a plurality of concentric tracks located on one of the first surface or the second surface. The plurality of concentric tracks include a first group of tracks written at a first track density, and a second group of tracks written at a second track density. The first track density is different than the second track density. If first track density is greater than the second track density, the first group of tracks is positioned nearer to the center of the disc than the second group of tracks. On the disc, the first group of tracks has information written at a different frequency that the information in the second group of tracks. A third group of tracks written at a third track density which is different than the first track density and the second track density is also contemplated. The track density for the first group is selected so that the percentage of track misregistration is substantially equal to a selected value. The track density for the second group is also selected so that the percentage of track misregistration is substantially equal to a selected value. In other words, the track density for the first group and the track density for the second group is selected so that the percentage of track misregistration is substantially equal to a selected value. In addition, the track density for the first group and the track density for the second group is selected in response to the percentage of track misregistration.
A disc drive is also disclosed which includes a base and a disc rotatably attached to the base. The disc has tracks for storing information. The disc drive also includes a movable actuator having a transducer positionable near said tracks, and a device for maintaining the percentage of occurrences of track misregistration between the track and the transducer to a selected range.
Advantageously, the disc drive which uses the above inventions has additional capacity. The disc for the disc drive allows additional information to be stored on the disc drive without an appreciable rise in the error rate. The disc is formatted to allow for additional data to be stored on the disc. The tracks per inch or track density of the groups of tracks on the disc of the disc drive serves to limit the amount of read and write errors that occur. As a result, the access times to information including customer data is unaffected by increased track density since the track density is selected so that the percentage of track misregistrations stays within a selected range. The result is that the disc in the disc drive is formatted so as not to allow the occurrence of track misregistration to climb over a selected percentage. Still a further advantage is that the method and apparatus used to format the disc in the disc drive do not deviate appreciably from current technologies. Therefore, the above inventions can be accommodated using manufacturing techniques close to current manufacturing techniques.